You can't judge a dot-com by its wrapper.

Priceline.com (Nasdaq: PCLN) and Orbitz Worldwide (NYSE: OWW) are two of the country's leading online travel websites. For a potential tourist seeking a cross-section of trip choices, the sites may seem similar in scope. But unfortunately for Orbitz, the two companies are moving in different directions.

Orbitz posted a wider loss and a 30% dip in adjusted EBITDA in its latest quarter, relative to last year's first-quarter showing. Revenue inched just 3% higher to $219 million. Gross bookings clocked in flat at $2.9 billion, with a surge overseas offsetting a 6% domestic decline.

The uninspiring showing was enough to trigger a Piper Jaffray downgrade and a 10% share-price slide on Thursday.

With Priceline set to report later that night, would the malaise be contagious? Not a chance.

Priceline's stock opened 12% higher on Friday, powered by yet another monster report representing everything that Orbitz wasn't. Revenue soared 34% to $403.2 million. Pro forma profits climbed 77% to $0.76 a share. Gross travel bookings were anything but flat, up a jaw-dropping 76%.

Sure, Priceline's biggest gains also came internationally, but it was no slouch closer to home. Domestic gross bookings were up 51%. Domestic airline ticketing was down at Orbitz, and clearly a lot of that business moved over to plump up Priceline's 83% gain.

How can two peers be so disparate? Is it better marketing -- those catchy William Shatner ads? Is it Priceline's gutsy move to do away with booking fees on full-priced airfare ticketing? Thrifty passengers may have been wooed by the "Name Your Own Price" bidding model that rests alongside Priceline's more conventional booking service. But that can't be the only explanation, because Orbitz also runs penny-pincher magnet CheapTickets.com.

Anything short of "all of the above" would be an incomplete answer.

The two reports fell on opposite ends of where Expedia (Nasdaq: EXPE) had landed a week earlier. The early bird's quarterly report found revenue and adjusted profits climbing 25% and 19%, respectively.

Priceline is the champ. There's no whiff of the stateside stench that investors are smelling at Orbitz, or even at travel deals publisher Travelzoo (Nasdaq: TZOO). The company's heady growth is likely to rival the reports out of China's Ctrip.com (Nasdaq: CTRP) and eLong (Nasdaq: LONG), when they report later this month. For those playing at home, Ctrip reports on Wednesday.

Once again, analysts can't keep up with Priceline. The company has trounced Wall Street's guesstimates in each of the past eight quarters. Priceline is now looking for pro forma profits to come in between $5.25 and $5.65 a share this year.

If history is any kind of teacher, three months from now, we'll be discussing how Priceline is still at the head of the class, with Orbitz unable to lose the dunce cap.

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Longtime Fool contributor Rick Munarriz has been booking travel online since the 1990s, but he does not own shares in any of the companies in this story. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.